The present invention relates to an apparatus for storing water separated from fuel. The present invention particularly relates to such a device in which the storage is reversible.
Through its combustion in engines, fuel provides the energy which is necessary for operating, for example, a motor vehicle. The timely and precisely quantified metering of the fuel into the combustion chamber, through either direct or indirect fuel injection, optionally with prior formation of a fuel-air mixture, is decisive for optimum power yield of the combustion and therefore minimal fuel consumption. For this purpose, injection systems which ensure this exact metering have been developed in recent years (for example, common rail systems, pump-nozzle systems, etc.). For this purpose, the fuel is always supplied under high pressure and at a high temperature.
Furthermore, the dimensions of the components which meter the fuel, such as nozzles, etc., have become ever smaller, for which reason these components must be effectively protected against blockage, even by small particles. This function is assumed by the fuel filter. It removes particles, which may arise, for example, from contamination of the fuel and the parts supplying the fuel during production, from external sources, or from wear, especially wear of metallic components such as pumps.
In addition to particles, the presence of water in the fuel may also have a negative effect on the parts supplying the fuel. Possible reasons for this include, for example, corrosion, reduced lubricant effect of the fuel, etc. The current limit for water dissolved in fuel is 200 ppm. However, this value may be significantly exceeded in practice. This may be caused by, among other things, condensation of water in storage tanks under the influence of large day/night temperature differences and/or very high ambient humidity, or in the course of filling the tanks themselves.
The water may be physically dissolved and/or emulsified. In addition, the solubility of water in fuel increases when alcohols or other components which contain oxygen are admixed into the fuel, as is the case in America, for example. Therefore, a modern fuel filter must, in addition to storing solid materials, also be able to effectively separate water present in the fuel.
This is currently achieved using modern filter media. The water is typically collected in a volume located in a filter and is removed using a drain plug after reaching the maximum fill level. However, since this water may still be contaminated with fuel residues, simply draining the mixture into the environment is not acceptable, i.e., methods for separating the water/fuel mixture must be found.
The different polarities of the liquids may be utilized to separate this mixture, whereby the water preferably is absorbed on a carrier material. This carrier material may be an organic or inorganic material or compound. A preferred solution to the problem is to use polymers such as polyacrylates, polyacrylic acids, polyacrylamides, polyesters, polysaccharides, and copolymers thereof, which have outstanding water storage ability (for example, up to more than 100 g of water per g of polymer for polyacrylates), caused by a high swelling capacity. This property is used, for example, in diapers and incontinence products. The products are commercially available, for example under the trade name HySorb (BASF).
It is additionally advantageous if the storage is reversible, i.e., when the water may be expelled again, for example by increasing the temperature or pressure. Since the nonpolar fuel may remain on the polymer in this case, separation of the mixture is achieved.
Thus, for example, Published German Patent Application No. DE 196 05 431 describes a filter for absorbing water from fuels, in which the polymer is contained in a composite filter which is accommodated in a filter housing. A disadvantage of this solution is that the space available for storage is much too small to store the quantities of water which may arise, for example, in a truck.